Method of manufacturing subminiature electric lamps

ABSTRACT

The lamp (which may be of the incandescent or photoflash type) has a composite envelope that is fabricated by sealing segments of light-transmitting and infrared-radiation absorbing glass tubing together in abutting relationship. The end of the infrared-radiation absorbing portion of the composite envelope is then hermetically sealed to the lead wires and the seal is formed by focusing a beam of infrared radiation onto the seal assembly. The envelope is evacuated, and filled with gas if desired, through its opposite end which is then tipped off. Oxidation of the lead wires is reduced to a minimum by forming the seal inside a chamber that is evacuated, or filled with an inert gas, and has walls which transmit infrared radiation. In the case of chambersealing, the free end of the light-transmitting portion of the envelope is sealed before the envelope-mount assembly is placed into the chamber so that the sealing and evacuation (or gas filling) operations are performed simultaneously.

United States Patent 1191 Boyce [54] METHOD OF MANUFACTURINGSUBMINIATURE ELECTRIC LAMPS [75] Inventor: Walter A. Boyce, Glen Ridge,NJ.

[73] Assignee: Westinghouse Electric Corp., Pittsburgh, Pa.

[22] Filed: Aug. 18, 1971 [21] Appl. No.: 172,673

Related US. Application Data [62] Division oi Ser. No. 889,663, Dec. 31,1969, Pat. No.

14 1 Feb. 13, 1973 Primary Examiner-Charles W. Lanham AssistantExaminer-D. M. Heist Attorney-A. T. Stratton et al.

[5 7] ABSTRACT The lamp (which may be of the incandescent or photoflashtype) has a composite envelope that is fabricated by sealing segments oflight-transmitting and infrared-radiation absorbing glass tubingtogether in abutting relationship. The end of the infrared-radiationabsorbing portion of the composite envelope is 3,636,398 thenhermetically sealed to the lead wires and the seal is formed by focusinga beam of infrared radiation [52] U.S.Cl. ..316/2l,65/58,65/138 Onto theseal essembly- The envelope is evacuated, [51] Int. Cl ..H01j 9/38, H0117/26 n fille with g if desired, through its opposite end [58] Field ofSearch ..3l6/l9, 20, 21, 24; 65/58, which is then tipped off. Oxidationof the lead wires is 65/138, 45 reduced to a minimum by forming the sealinside a chamber that is evacuated, or filled with an inert gas, [56]References Cited and has walls which transmit infrared radiation. In thecase of chamber-sealing, the free end of the light- UNITED STATESPATENTS transmitting portion of the envelope is sealed before 3,537,27611/1970 Pityo ..65/59 the envelope-mount assembly is placed into the3,409,342 /1968 nderson etalm ...-.316/24 chamber so that the sealingand evacuation (or gas Brundige operations are performed simultaneously3,416,851 12/1968 Palermo et al. ..3l6/l9 6 Claims, 7Drawing Figures "'1,1 IB .q -/'25 METHOD OF MANUFACTURING SUBMINIATURE ELECTRIC LAMPSCROSS-REFERENCES TO RELATED APPLICATIONS The present application is adivision of application Serial No. 889,663, filed Dec. 31, 1969 (nowU.S. Pat. No. 3,636,398) and, broadly considered, is also related to thesubject matter disclosed in the commonly-assigned application Ser. No.805,231 of W. L. Brundige filed March 7, 1969 and entitled Method ofTipping Off the Exhaust Tube of an Electric Lamp, And A BaselessSingle-Ended Incandescent Lamp Produced By Such Method (now U.S. Pat.No. 3,551,725).

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to electric lamps and has particular reference to animproved method for manufacturing subminiature lamps of the incandescentor photoflash type.

2 Description of the Prior Art Electric lamps of extremely small sizeare well known in the art and are referred to as subminiature ormicrominiature lamps. Because of their small dimensions, such lamps aredifficult to manufacture and present quality control problems which arenot encountered in larger size lamps. A microminiature incandescent lamphaving an envelope that is sealed by a glass bead which is melted bypassing electric current through the filament and lamp leads during thesealingin operation is disclosed in U.S. Pat. No. 3,275,879 issued Sept.27, 1966, to PC. Demarest et al. Another incandescent lamp of this typehaving a quartz envelope that is sealed by heating the quartz and presssealing it around the lead-in conductors is described in U.S. Pat. No.3,462,209 issued Aug. 19, 1969, E.G. Fridrich. A microminiaturephotoflash lamp having an envelope which is sealed by a glass bead whichis fused to the mouth of the envelope by sharply-defined :saling firesis disclosed in U.S. Pat. No. 3,263,457, issued Aug. 2, 1966, to H.Reiber.

While. satisfactory lamps can be made using such techniques, theyrequire accurately-dimensioned interfitting envelopes and beads or theuse of gas sealing fires and pressing-sealing operations which aredifficult to control due to the extremely small size of the parts beingjoined. Unless adequate precautions are taken, the combustion productsof the sealing fires will contaminate the finished lamps and excessiveoxidation of the metal parts of the lamps can easily occur which maycause leaky seals.

OBJECTS AND SUMMARY OF THE INVENTION It is accordingly the generalobject of the present invention to provide a convenient and practicalmethod for manufacturing an electric lamp of the subminiature ormicrominiature type.

A more specific object is the provision of a method for manufacturingsuch lamps without the use of sealing fires, press-forming operations,or accuratelyformed interfitting glass beads or the like that make itdifficult and time-consuming to assemble the lamps and create conditionsduring the sealing-in operation which could contaminate the lamp orbadly oxidize the lead wires or filament.

The foregoing objectives and other advantages are achieved in accordancewith the present invention by making the end segment of the envelopefrom infraredabsorbing glass and sealing it to the lead-in wires withinfrared radiation that is focused onto the seal assembly. In accordancewith one embodiment, the filament mount is sealed into one end of thecomposite envelope with infrared energy and the envelope is evacuatedthrough its opposite end which is then tipped off with conventionalsealing fires.

In another embodiment, oxidation of the lead wires during the sealing-inoperation is practically eliminated by placing the composite envelopeand filament mount in ealing relationship within an enclosure that hasinfrared-transmitting walls and is evacuated. The infrared energy sourceis located outside the enclosure and the infrared radiation istransmitted through the walls of the enclosure and focused onto the endof the envelope to form the hermetic seal, thus completing the lamp. Thechamber can be filled with a suitable inert gas, such as nitrogen or thelike, to provide a gas-filled lamp if desired. Since the lamp isconcurrently evacuated (or gas filled) and sealed in accordance withthis embodiment, the opposite end of the envelope is sealed off when thecomposite envelope is formed. Preformed envelopes having flat or domedends can thus be used.

In either case, the envelope is sealed to the lead wires in a veryconvenient and efficient manner without the use of gas-sealing fires oraccurately dimensioned beads or the like.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the inventionwill be obtained by referring to the accompanying drawings, wherein:

FIG. 1 is an enlarged side elevational view of a subminiatureincandescent lamp made in accordance with the present invention;

FIGS. 2(a) to 2(d) are elevational views illustrating the various phasesin the manufacture of the composite envelope employed in the lamp shownin Fig. 1;

FIG. 3 is an elevational view, partly in section, illustrating theapparatus and procedure employed to seal another sealing apparatus whichpermits the seal to be effected'in an evacuated or gas-filled chamber;and,

FIG. 7 is a plan view of a similar apparatus wherein three projectionlamps are used as exterior infraredgenerating sources.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 there is shown asubminiature incandescent lamp 10 of the type produced by the presentinvention. As noted, it consists of a composite tubular envelope 11having a light-transmitting body portion 12 that'is terminated at oneend by a protruding seal tip 13 of fused glass and at its opposite endby a fused body 14 of infrared-absorbing glass. The glass body 14 ishermetically sealed to a pair of lead-in conductors 16, such as dumetwires, that are fastened to an incandescible filament 17 and hold itwithin the light-transmitting portion 12 of the envelope 11. Thefilament 17 comprises a coil of suitable refractory wire such astungsten that is connected as by spot welding to the inner ends of theleadin wires 16. The latter are preferably composed of dumet" wire andare of such rigidity that the filament 17 is supported within theenvelope l1 solely by the lead-in wires. A glass stem or head isaccordingly not required. Dumet" wire is well known in the art andconsists of a nickel-iron core wire that is clad with copper and thenheat treated to controllably oxidize the copper surface. The core wireand copper cladding are bonded together metallurgically so that thecomposite wire has a continuous metal structure. The core wire givesstrength to the dumet and its expansion as close to that of the softglasses, such as lead glass, which are used in the envelopes ofsubminiature lamps of this type.

The term subminiature as used herein and in the dependent claims refersto electric lamps having an overall length less than about 25millimeters and a maximum envelope diameter less than about 10millimeters and includes within its scope lamps of very small dimensionsthat are referred to in the art as microminiature lamps. The lamp 10shown in FIG. 1 had an overall length of approximately 10 millimetersand employed a T1 envelope having an outside diameter of approximately 3millimeters.

As a specific example of suitable glasses, the lighttransmitting portion12 of the envelope 11 is composed of a soda-lead glass well known in theart. A typical formulation for such a glass is as follows: 62.7 percentSi 6.8 percent Na O, 6.6 percent K 0, 21.8 percent PbO, 1.7 R 0, and 0.4percent incidental impurities (where R 0 is one or more additionalalkali metal oxide such as U0.)

The fused end segment 14 of the envelope 11 is composed of a suitableinfrared-absorbing glass that contains a small but sufficient amount ofiron oxide to render the glass infrared absorbing. Suchinfrared-absorbing glasses are also well known in the art and arecommercially available as Corning Code 9362 and Code 9363 sealingglasses. The glasses are greencolored potash-soda-lead glasses that haveviscosity and expansion characteristics that are almost identical withCorning Code 0120 soda-lead glass so that the end segment 14 of theenvelope 11 can be readily sealed to the light-transmitting body portion12. The information published by Corning indicates that Code 9362 andCode 9363 glasses have very high energy absorption in the infraredregion from approximately I to 4 microns wavelength and that Code 9363glass has lower expansion characteristics which make it superior to Code9362 glass for sealing to dumet wire. Thus, an end segment 14 made ofeither of these glasses can be quickly heated and fused to the lead-inwires 16 by a focused beam of infrared radiation.

Transparent infrared-absorptive sealing glasses such as those disclosedin U.S. Pat. No. 3,445,256, issued May 20, 1969, which contain selectedamounts of PbO, si0,, Fe o and alkali metal oxides can also be used.

The various operations in fabricating the composite envelope 11 areshown in FIGS. 2(a) to 2(d) and will now be described. As illustrated inFig. 2(a), the envelope 11 includes a segment 12 of suitable soda-leadglass tubing and a shorter tube segment 14' that is of the same diameterbut composed of infrared-absorbing glass. One end of the soda-lead glasstubing 12' is heatsoftened and partially collapsed to form aconstriction 18, as shown in Fig. 2(b). The tube segments 12' and 14'are then placed in end-to-end abutting relationship and the oppositeends of the segments are temporarily closed off from the atmosphere byrubber caps 19 and 20 or the like, as illustrated in Fig. 2(0). Theabutting portions of the tube segments are then sealed together by asuitable gas fire (not shown), thus forming the composite envelope 11shown in Fig. 2(d). The softened abutting ends of the segments 12' and14 are prevented from collapsing inwardly during the sealing operationby the air which is trapped within the tubes by the caps 19 and 20.

As shown in FIG. 3, the resulting composite envelope 1 1 is then placedover a filament mount that comprises the spaced lead-in wires 16 andjoined filament 17. The mount is held in upstanding position within theenvelope 11 by inserting the ends of the lead wires 16 into a head 22that has pockets 23 and 24 which nestingly accommodate the ends of thewires. The envelope 11 is maintained in sealing relationship with thefilament mount by a suitable holder 25 that grips the upper end of theenvelope. The end segment 14 is then melted and collapsed down onto theunderlying portions of the lead-in wires 16 by energizing a suitableinfrared-energy source 26 and concentrating the infrared radiation intoa beam 31 that is focused onto the segment 14. In the embodiment shownin FIG. 3, the infrared-radiation source 26 comprises a 500 watt T12focus beam projection lamp that has a coiled tungsten filament 28 and aninternal reflector 30 which concentrates the infrared energy into afocused beam 31.

As shown in Fig. 4, three 500 watt focused beam" type projection lamps26, 32 and 33 are preferably used and are spaced approximately apartaround the seal assembly so that the beams 31 of infrared energy arefocused onto the end segment 14 of the envelope 11 and rapidly anduniformly heat the glass to its melting temperature. With thisarrangement, an hermetic glass-to-metal seal was formed withinapproximately 15 seconds in the case of the aforesaid T1 type envelope.Any source of infrared energy having means for focusing the radiationscan be used. Thus, a suitable reflector and a halogen type infraredincandescent lamp of sufficient wattage could be used in place of theaforementioned focused beam" type projection lamps.

The resulting sealed-in lamp 10' is then evacuated by connecting theopen end of the envelope 11 to a suitable exhaust system (not shown) andthe constriction 18 is tipped off with a sharply-defined gas flame inthe usual manner, thus producing the finished lamp 10 shown in FIG. 1. Asuitable inert fill gas, such as nitrogen or the like at one or severalatmospheres pressure, can be introduced into the envelope 11 after ithas been evacuated and before it is tipped off to provide a gas-filledlamp, if desired.

The present invention can also be employed to manufacture subminiaturephotoflash lamps. This can readily be accomplished by placing a suitableactinic fuel, such as a weighed amount of shredded zirconium, into theenvelope 11 near the constriction 18 before the envelope is placed overthe filament mount and sealed to the lead-in wires 16. In this case, thefilament 17 need not be coiled but can consist of a straight piece offine tungsten wire which preferably extends beyond the tips of the leadwires. A suitable ignition material or primer may be applied to thetungsten filament or to the tips ofthe lead wires 16 in accordance withconventional photoflash lamp-making practice. Of course, the envelope 11in this case is also filled with oxygen at a suitable pressure such asatmospheres and a protective plastic coating is applied to the exteriorsurface of the envelope 11 to prevent it from shattering when thephotoflash lamp is fired.

ADDITIONAL EMBODIMENT (FIGS. 6-7) In FIG. 6 there is shown anotherembodiment of the invention which enables a subminiature electric lampto be simultaneously sealed and evacuated, or filled with a suitableinert gas. This embodiment also enables pre-blown composite envelopes11a to be used. As shown, the end of the light-transmitting tubularportion 12a of such an envelope is sealed during the bulb-makingoperation by heating and molding it into a smooth dome 15.

As before, the filament mount is supported in upstanding position withinthe envelope lla by a head 220 having a pair of pockets 23a and 24awhich nestingly receive the ends of the lead wires 16a. The domedcomposite envelope 11a is supported in enclosing'and sealingrelationship with the filament mount by a bulb-holder 34 that isadjustably fastened to a support arm 35 anchored to the head 22a. Theentire assembly is protected from the atmosphere by an enclosure 36 thatis composed of a suitable infrared-transmitting material, such as quartzor Vycor glass, and is hermetically joined to the peripheral edge of thehead 22a. The

resulting air-tight chamber is evacuated through a suitable conduit 38that extends through the head 22a and sealing of the infrared-absorbingglass portion 14a of the envelope 11a is achieved by energizing anexterior source of infrared radiation, such as a focused beam typeprojection lamp 26, and directing the focused beam 31 of infraredradiation through the side wall of the enclosure 36 onto the sealassembly.

Oxidation of the lead-in wires 16 during the sealingin operation is, ofcourse, practically eliminated with this technique since the fusion ofthe envelope end segment 14a with the lead wires 16a is accomplished ina vacuum. If a gas-filled lamp 10a is desired, then the enclosure 36 isfilled with a suitable inert gas at the desired pressure after thechamber is evacuated and before the sealing-in operation is begun.

As will be noted in FIG. 7, equidistantly spaced sources of infraredenergy, such as three focused beam projection lamps 26, 32 and 33, arepreferably employed since this effects uniform heating of the glasssegment 14a and reduces the time required to complete the seal.

It will be appreciated from the aforesaid that the objects of theinvention have been achieved in that a very simple and practical methodand apparatus have been fastening a pair of lead wires to anincandescible filament to form a self-supporting mount,

holding said mount by the free ends of said lead wires, placing thecomposite envelope over and in enclosing relationship with said mount sothat the infrared-absorbing portion of said envelope encircles saidwires at a location remote from said filament, holding said envelope andfilament mount in such position and concurrently focusing infraredradiation onto the infrared-absorbing glass portion of the envelope tomelt the latter and form a hermetic seal with the underlying portions ofsaid lead wires,

evacuating said envelope through the open end thereof, and then heatingand sealing off the open end of said envelope.

2. The method of claim 1 wherein;

said composite envelope is of elongated tubular configuration,

an end segment of the light-transmitting portion of said compositeenvelope is locally heated and partially collapsed to form aconstriction, and

said envelope is subsequently sealed off by heating and tipping off saidconstriction.

3. The method of claim 1 wherein said lamp comprises subminiaturephotoflash lamp and said envelope is charged with actinic fuel andfilled with oxygen prior to being sealed off.

4. The method of claim 1 wherein;

the free ends of said hollow member of light-transmitting glass and saidsegment of infrared-absorbing glass tubing are temporarily sealed offfrom the atmosphere while being sealed together, and

the melting of the infrared-absorbing end portion of said envelope andthe formation of the hermetic seal with the lead wires is achieved byplacing three infrared-generating incandescent lamps at substantiallyequidistantly spaced locations around the envelope and focusing thegenerated infraredradiations onto the infrared-absorbing end portion ofsaid envelope.

5. The method of manufacturing a subminiature electric lamp comprising;

sealing a hollow member of light-transmitting glass in abuttingend-to-end relationship with a segment of infrared-absorbing glasstubing to form a composite envelope,

heating the free end of said light-transmitting glass member toplasticity and forming a smooth domeshaped end wall that closes that endof the envelope,

fastening a pair of lead wires to an incandescible filafrared-absorbingend portion of the envelope,

ment to form a self-supporting mount, evacuating said air-tightenclosure, and holding said mount by the free ends of said lead passinginfrared radiation through the said wall of the wires, enclosure andfocusing said radiation onto the inplacing the composite envelope oversaid mount and flared-absorbing end portion of said envelope to h ldingthe e v l in enclosing l i hi thereby melt the latter and form anhermetic seal therewith to provide an envelope-mount assembly with theunderlymg P01110115 l f wherein the infrared-absorbing end portion ofthe methoq of clfum 5 where!" 531d 8 envelope encircles Said lead wiresat a location closure is filled with an inert gas after it has beenevacuremote f Said fil t l0 ated and before the hermetic seal is formedso that the placing said envelope moum assembly within an completed lampcontains an atmosphere of said inert tight enclosure which has aninfrared-radiation transmitting wall that is located adjacent the in-

1. The method of manufacturing a subminiature electric lamp comprising:sealing a hollow member of light-transmitting glass in end-to-endabutting relationship with a segment of infrared-absorbing glass tubingto form a composite glass envelope, fastening a pair of lead wires to anincandescible filament to form a self-supporting mount, holding saidmount by the free ends of said lead wires, placing the compositeenvelope over and in enclosing relationship with said mount so that theinfrared-absorbing portion of said envelope encircles said wires at alocation remote from said filament, holding said envelope and filamentmount in such position and concurrently focusing infrared radiation ontothe infrared-absorbing glass portion of the envelope to melt the latterand form a hermetic seal with the underlying portions of said leadwires, evacuating said envelope through the open end thereof, and thenheating and sealing off the open end of said envelope.
 2. The method ofclaim 1 wherein; said composite envelope is of elongated tubularconfiguration, an end segment of the light-transmitting portion of saidcomposite envelope is locally heated and partially Collapsed to form aconstriction, and said envelope is subsequently sealed off by heatingand tipping off said constriction.
 3. The method of claim 1 wherein saidlamp comprises subminiature photoflash lamp and said envelope is chargedwith actinic fuel and filled with oxygen prior to being sealed off. 4.The method of claim 1 wherein; the free ends of said hollow member oflight-transmitting glass and said segment of infrared-absorbing glasstubing are temporarily sealed off from the atmosphere while being sealedtogether, and the melting of the infrared-absorbing end portion of saidenvelope and the formation of the hermetic seal with the lead wires isachieved by placing three infrared-generating incandescent lamps atsubstantially equidistantly spaced locations around the envelope andfocusing the generated infrared-radiations onto the infrared-absorbingend portion of said envelope.
 5. The method of manufacturing asubminiature electric lamp comprising; sealing a hollow member oflight-transmitting glass in abutting end-to-end relationship with asegment of infrared-absorbing glass tubing to form a composite envelope,heating the free end of said light-transmitting glass member toplasticity and forming a smooth dome-shaped end wall that closes thatend of the envelope, fastening a pair of lead wires to an incandesciblefilament to form a self-supporting mount, holding said mount by the freeends of said lead wires, placing the composite envelope over said mountand holding the envelope in enclosing relationship therewith to providean envelope-mount assembly wherein the infrared-absorbing end portion ofthe envelope encircles said lead wires at a location remote from saidfilament, placing said envelope-mount assembly within an air-tightenclosure which has an infrared-radiation transmitting wall that islocated adjacent the infrared-absorbing end portion of the envelope,evacuating said air-tight enclosure, and passing infrared radiationthrough the said wall of the enclosure and focusing said radiation ontothe infrared-absorbing end portion of said envelope to thereby melt thelatter and form an hermetic seal with the underlying portions of saidlead wires.